1. Field of the Invention
This invention relates to tungsten and tungsten nitride coatings for metal and ceramic substrates.
2. Description of the Prior Art
Refractory metal coatings have been used in a number of applications. These include aerospace, defense, and cutting tools. Materials to which refractory metal coatings have been applied include powders, monoliths, and fibers. Most refractory metal coatings are applied either by thermal evaporation, thermal spraying, physical vapor deposition, (sputtering) or chemical vapor deposition. For instance, the application of metal halides in a reducing atmosphere, such as tungsten hexafluoride in a hydrogen atmosphere. The first two techniques are energy intensive, sputtering is often slow and involves high-cost equipment, and chemical vapor deposition processes are often undesirable due to the formation of hydrohalic acid vapor as a by-product. In U.S. Pat. No. 3,394,087, a vitreous enamel resistance material is coated onto a substrate by brushing, dipping, spraying, or screen stencil application and subsequently fired in an inert atmosphere or a reducing atmosphere. The resistance material can contain, as a component, tungsten nitride in combination with a glass frit, such as, barium or calcium borosilicate. The mixture is prepared for application by ball-milling.
In U.S. Pat. No. 4,120,930, a mold of a ceramic material is coated with a metallic layer by spray, electrolytic, or electroless application of a solution containing powdered metal or alternatively coated by electroless deposition employing solvated aluminum hydride.
In U.S. Pat. No. 4,820,562, a metalizing composition is applied to a sintered ceramic article from a solution containing metal salts of tungstic acid in combination with an oxide, boride, carbide, and organic metal compounds of a transition metal Group IVb of the Periodic Table of the Elements. The metallizing composition is used in the form of a liquid or paste which contains a binder, such as, ethyl cellulose and water as the liquid. Subsequent to application of this coating, the dried coating is fired in a non-oxidizing atmosphere.
Sarin et al disclose the preparation of improved cutting tools and cutting tool inserts in U.S. Pat. No. 4,441,894. Physical vapor deposition or chemical vapor deposition techniques are used to apply refractory materials to a composite silicon nitride substrate.
Other methods of protecting ceramic or metal bodies against mechanical and thermal action are disclosed in U.S. Pat. Nos. 4,828,934; 4,011,064; 4,847,111; 3,637,422; and 4,714,660.
Nugent et al in Inorganic Chemistry 1980, 19, 777 disclose preparation of an organoimido complex produced by reacting tungsten hexachloride with tert-butylamine in hexane. No suggestion for the use of this complex is disclosed.